Researchers in Japan have transformed mosquitoes into vaccine-carrying syringes by genetically engineering the insects to express the vaccine for leishmaniasis--a parasitic disease transmitted by the sandfly--in their saliva. According to a study in Insect Molecular Biology, mice bitten by these mosquitoes produced antibodies against the parasite. It's not yet clear whether the immune response was strong enough to protect against infection.

"Following bites, protective immune responses are induced, just like a conventional vaccination but with no pain and no cost," said lead researcher Shigeto Yoshida, from the Jichi Medical University in JapanYoshida, in a press release from the journal. "What's more continuous exposure to bites will maintain high levels of protective immunity, through natural boosting, for a life time. So the insect shifts from being a pest to being beneficial."

Researchers consider the project more of a proof of principle experiment than a viable public health option, at least for now. According to an article on ScienceNow,

There's a huge variation in the number of mosquito bites one person received compared with the next, so people exposed to the transgenic mosquitoes would get vastly different doses of the vaccine; it would be a bit like giving some people one measles jab and others 500 of them. No regulatory agency would sign off on that, says molecular biologist Robert Sinden of Imperial College London. Releasing the mosquitoes would also mean vaccinating people without their informed consent, an ethical no-no. Yoshida concedes that the mosquito would be "unacceptable" as a human vaccine-delivery mechanism.

However, flying vaccinators-or "flying syringes" as some have dubbed them -may have potential in fighting animal disease, says [David O'Brochta, an insect molecular geneticist at the University of Maryland, College Park]. Animals don't need to give their consent, and the variable dosage would be less of a concern.